Triangular numbers that are sandwiched between two squarefree semiprimes.

Terms

a(0) =300a(1) =780a(2) =2628a(3) =3240a(4) =3828a(5) =5460a(6) =13530a(7) =18528a(8) =19110a(9) =22578a(10) =25878a(11) =31878a(12) =32640a(13) =37128a(14) =49770a(15) =56280a(16) =64980a(17) =72390a(18) =73920a(19) =78210a(20) =103740a(21) =105570a(22) =115440a(23) =137550a(24) =159330a(25) =161028a(26) =277140a(27) =288420a(28) =316410a(29) =335790